1. Field of the Invention
This present invention relates to new, solid state designs for rechargeable oxide-ion battery (ROB) cells.
2. Description of Related Art
Electrical energy storage is crucial for the effective proliferation of an electrical economy and for the implementation of many renewable energy technologies. During the past two decades, the demand for the storage of electrical energy has increased significantly in the areas of portable, transportation, load-leveling and central backup applications. The present electrochemical energy storage systems are simply too costly to penetrate major new markets. Higher performance is required, and environmentally acceptable materials are preferred. Transformational changes in electrical energy storage science and technology are in great demand to allow higher and faster energy storage at lower costs and longer lifetimes necessary for major market enlargement. The nature of variable electricity production by renewable energy resources requires an effective means of storing surplus renewable energy for peak utility consumption (“peak shaving”) in order for the entire energy system to be reliable and efficient. Most of these changes require new materials and/or innovative concepts, with demonstration of larger redox capacities that react more rapidly and reversibly with cations and/or anions.
Batteries are by far the most common form of storing electrical energy, ranging from: standard every day lead-acid cells, nickel-metal hydride (NiMH) batteries taught by Kitayama in U.S. Pat. No. 6,399,247 B1, metal-air cells taught by Isenberg in U.S. Pat. No. 4,054,729, and to the lithium-ion battery taught by Ohata in U.S. Pat. No. 7,396,612 B2. These latter metal-air, nickel-metal hydride and lithium-ion battery cells require liquid electrolyte systems.
Batteries range in size from button cells used in watches, to megawatt load leveling applications. They are, in general, efficient storage devices, with output energy typically exceeding 90% of input energy, except at the highest power densities. Rechargeable batteries have evolved over the years from lead-acid through nickel-cadmium and nickel-metal hydride (NiMH) to lithium-ion batteries. NiMH batteries were the initial workhorse for electronic devices such as computers and cell phones, but they have almost been completely displaced from that market by lithium-ion batteries because of the latter's higher energy storage capacity. Today, NiMH technology is the principal battery used in hybrid electric vehicles, but it is likely to be displaced by the higher power energy and now lower cost lithium batteries, if the latter's safety and lifetime can be improved. Of the advanced batteries, lithium-ion is the dominant power source for most rechargeable electronic devices.
What is needed is a dramatically new electrical energy storage device that can easily discharge and charge a high capacity of energy quickly and reversibly, as needed. What is also needed is a device that can operate for years without major maintenance. What is also needed is a device that does not need to operate on natural gas, hydrocarbon fuel or its reformed by-products such as H2 and CO. One possibility is a rechargeable oxide-ion battery (ROB), as set out, for example, in Siemens application Ser. No. 12/695,386, filed on Jan. 28, 2010, and Siemens application Ser. No. 12/876,391, filed on Sep. 7, 2010.
A ROB comprises a metal electrode, an oxide-ion conductive electrolyte, and an air electrode which air contacts. The metal electrode undergoes reduction-oxidation cycles during charge and discharge processes for energy storage. For example, in discharging mode, the metal is oxidized:yMe+x/2O2=MeyOx and is reduced in charging mode:MeyOx=x/2O2+yMe, where Me=metal.
Because the metal redox reactions are accompanied by large volume variation, for instance, if manganese (Mn) metal is used, the volume change associated with reaction of Mn+½O2=MnO is 1.73 times. In the case of tungsten (W), the volume change is 3.39 times when W is totally oxidized to WO3. Without appropriately designed electrode, such drastic volume variation in practice can lead to spallation of metal electrode and possible failure of a ROB cell. The electrode, comprising a porous structural skeleton with the attached active metal component on its wall has been considered as an effective solution to address the volume issue. The skeleton is made of single and/or multiple components and is capable of conducting electrical current, and it contains active metal component in its pores. The skeleton maintains its structural integrity by accommodating the volume change associated with metal redox reactions in its pores.
The metal electrode must meet the following requirements to be effective in practice. It must be compatible with adjacent components including electrolyte and interconnect during battery fabrication and operation in terms of minimal mismatch in coefficient of thermal expansion and negligible chemical reactions with the electrolyte and interconnect. It must possess adequate electrical conductivity to minimize its Ohmic loss. It must possess sufficient catalytic activity to promote metal redox reaction to reduce polarization losses.
The working principles of a rechargeable oxide-ion battery cell 10 are schematically shown in FIG. 1. In discharge mode, oxide-ion anions migrate from high partial pressure of oxygen side (air electrode-12) to low partial pressure of oxygen side (metal electrode-14) under the driving force of gradient of oxygen chemical potential. There exist two possible reaction mechanisms to oxidize the metal. One of them, solid-state diffusion reaction as designated as Path 1, is that oxide ion can directly electrochemically oxidize metal to form metal oxide. The other, gas-phase transport reaction designated as Path 2, involves generation and consumption of gaseous phase oxygen. The oxide ion can be initially converted to gaseous oxygen molecule on metal electrode, and then further reacts with metal via solid-gas phase mechanism to form metal oxide. In charge mode, the oxygen species, released by reducing metal oxide to metal via electrochemical Path 1 or solid-gas mechanism Path 2, are transported from metal electrode back to air electrode. To enable the electrochemical reactions listed in FIG. 1, the electrical current must be conducted sufficiently along its path including the metal electrode. Thus, electrically conductive materials must be used to produce the metal electrode. The candidate metal negative (anode) electrode materials for the ROB cell include electrically conductive ceramics such as doped LaCrO3, doped SrTiO3, and doped LaVO3.
Different from the metal electrode where oxygen is stored in condensed phases, the oxygen electrode does not contain the reactive oxygen species in a chemical. Instead, oxygen molecules submerge into or emerge from a flowing air reservoir, retaining a constant partial pressure of oxygen during operational cycles. One advantage of such a design is that air can be used as a means of regulating temperature distributions within the battery stack during the exothermic discharging and endothermic charging cycles. However, the use of hot air requires peripheral subsystems to support on-demand variable air flows. Uncontrollable air leakage into the negative electrode could easily consume all the active metals and result in a complete loss of the performance. The ultimate consequences of these drawbacks are the lowered performance, reduced efficiency and increased system cost.
Therefore, there is a great need to advance the current ROB by an alternative design to eliminate the use of air at the oxygen electrode in order to meet the targets of performance, cost and reliability.
It is a main object of this invention to provide cost effective all solid-state ROB cell eliminating the need for air at the oxygen electrode.